1. Field of Invention
The present invention relates to an aluminum electrolytic capacitor for various electronic devices, and to a method for producing the same.
2. Prior Art
FIG. 3 shows one constitution of conventional aluminum electrolytic capacitors. A capacitor element 39 is formed such that an anode foil 31 on which a dielectric oxide layer is formed by anodizing a surface which have increased in effective surface area by etching and a cathode foil 32 currently made of an aluminum foil which is etched are wound through a separator 33 made of a Kraft paper or Manila paper, etc. disposed there between.
In the capacitor element 39, an anode lead 35 and a cathode lead 36 are connected to the anode foil 31 and the cathode foil 32, respectively, and a driving electrolytic solution 34 is infiltrated into them. The capacitor element 39 is inserted into a metal case 38, such as an aluminum case, which subsequently is sealed by a sealing plate 37 made of rubber to complete an aluminum electrolytic capacitor.
The electrolytic solution 34 including boric acid or ammonium borate as a solute in organic solvent has been conventionally known. As other organic solutes, dibasic acid, such as azelaic acid, butyl octanedioic acid, 5,6-decane dicarboxylic acid, and dibasic acids having side chains, and their salts have been also used. These organic carboxylic acids have an advantage of reducing content of water in the driving electrolytic solution 34, therefore are able to suppress a phenomenon of a safety plug of the case breaking out by increased internal pressure of water content under operation environments exceeding 100xc2x0 C.
Moreover, in driving electrolytic solutions for driving 34, surfactant have been added for the purpose of increasing a spark generating voltage of electrolytic solution, and improving anodizing performance. Polyethylene glycol (Japanese Patent Publication No. 62-268121), polyglycerine (Japanese Patent Publication No. 02-194611), polyvinyl alcohol (Japanese Patent Publication No. 02-051209), and alkylene block polymers (Japanese Patent Publication No. 02-312218) have been disclosed as surfactants.
Moreover, a technique of adding a gelling agent to an electrolytic solution in the light of leak suppression is also described in Japanese Patent Publication No. 02-014506. However, the gelling agents known until now are agar, cellulose, and gelatin, which have inadequate heat resistance, these materials can not keep stable shapes at a high temperature. Further, adding of a polymer alone showed insufficient uniformity.
However, aluminum electrolytic capacitors used for suppressing higher harmonics and/for vehicles in recent years are required to have, a high reliability over conventional capacitors including a higher breakdown voltage, a higher heat resistance, a longer life, and excellent vibration resistance property.
Conventional electrolytic solutions in which organic carboxylic acid or salt as a solution and the surfactant are added cannot satisfy the above described requirements, and a new electrolytic solution is required to satisfy high breakdown voltage, i.e., improve spark generating voltage, a high heat resistance, and a long life.
An aluminum electrolytic capacitor in which a capacitor element is fixed inside a metal case by a fixing member made of resin is also proposed so that it may not easily vibrate by external impact. The fixing member is formed with a thermoplastic resin, such as atactic polypropylenes, but an increase in ambient temperature on the electrolytic capacitor softens the fixing member, and vibration applied oscillates the capacitor element relative to the container, and thereby occasionally, this vibration breaks leads from the capacitor elements, resulting in loss of capacitor functions.
An object of the present invention is, to solve the conventional problems above, to provide an aluminum electrolytic capacitor to improve reliability with high breakdown voltage, high heat resistance and long life, and to provide a method for producing the same.
Another object of the present invention is to provide an aluminum electrolytic capacitor in which a capacitor element has a high vibration resistance in a metal case even at relative high temperatures.
In the aluminum electrolytic capacitor of the present invention, heat-resistant gel-like polymer is used in which an electrolytic solution is infiltrated as an electrolyte. The electrolytic solution infiltrated gel-like polymer contains an electrolytic solution and a polymer in which the electrolytic solution is infiltrated, the gel-like polymer is included inside a capacitor element formed such that an anode foil, a cathode foil, and a separator placed among them are wound, and placed inside a metal case, and thereby high heat resistance and high breakdown voltage are produced in the aluminum electrolytic capacitor.
In the capacitor of the present invention, gel-like high infiltrated with an electrolytic solution polymer is filled not only inside the capacitor element but in a clearance between an external surface of the capacitor element, and an internal surface of a cylindrical metal case having a bottom so that the capacitor element can be firmly fixed inside the metal case. This provides high vibration resistance property for the capacitor.
Especially, as a gel-like polymer can be given characteristics not easily to be softened at higher temperatures than room temperature, the capacitor may have good vibration resistance property even at so high temperatures.
In the present invention, the gel-like polymer shows a semi-solid-state after infiltration of an electrolytic solution, and constructs a skeleton having many pores in which a conductive electrolytic solution may be impregnated.
The present invention includes a method of producing an aluminum electrolytic capacitor using a heat-resistant conductive gel-like polymer as an electrolyte. The method of producing the capacitor of the present invention comprises steps of: preparing a coil-like capacitor element by winding an anode foil, a cathode foil, and a separator in between the electrodes; infiltrating the capacitor element with a mixed solution of an electrolytic solution and a gelling agent, and placing the capacitor element in a metal case to fabricate an assembly; and heating the assembly to gelate the gelling agent in the case.
In the method for production of the present invention, polymerizable monomers are included in the gelling agent and after placing the capacitor element into the case, the assembly is heated to polymerize the monomers. Thus obtained gel-like polymer can firmly attach the capacitor element to an internal surface of the metal case, then the capacitor is stabilized in the case, and, as a result, an aluminum electrolytic capacitor having superior vibration resistance property may be provided.